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In 2019, an agency within the U.S. Department of Defense put out a call for research projects to help the military deal with the massive amounts of plastic waste generated when troops are sent to remote or disaster areas. The agency wanted a system that could convert food packaging and water bottles, among other things, into usable products like fuel and rations. The system had to be small enough to fit in a Humvee and use little energy. It also had to harness the power of plastic-eating microbes.
“When we started this project four years ago, the ideas were there. And theoretically it made sense,” says Stephen Techtmann, a microbiologist at Michigan Technological University who leads one of the three research groups receiving the funding. Still, he says, at first the venture felt “much more like science fiction than something that would actually work.”
That uncertainty was critical. The Defense Advanced Research Projects Agency (DARPA) supports high-risk, high-reward projects. That means there's a good chance that every single effort will fail. But if a project succeeds, it has the potential to be a real scientific breakthrough. “Our goal is to go from skepticism of, 'This is a joke. What are you going to do?' to, 'You know, this might actually be doable,'” said Leonard Tender, a program manager at DARPA who oversees the plastic waste projects.
The problems associated with the production and disposal of plastic are well known. According to the United Nations Environmental Programme, around 440 million tonnes of plastic waste are produced worldwide each year. Much of this ends up in landfills or in the ocean, where microplastics, plastic pellets and plastic bags pose a threat to wildlife. Many governments and experts agree that reducing production is necessary to solve the problem. Some countries and US states have also introduced measures to promote recycling.
Scientists have also been experimenting with different types of plastic-eating bacteria for years. But DARPA is taking a slightly different approach and is looking for a compact and mobile solution that uses plastic to make something completely different: food for people.
The goal, Techtmann quickly adds, is not to feed people plastic. Rather, he hopes the plastic-eating microbes in his system will prove themselves fit for human consumption. While Techtmann believes the project will be largely complete in a year or two, this food step could take longer. His team is currently conducting toxicity tests and will then submit the results to the Food and Drug Administration for review. Even if all goes well, there is still another challenge. There is a gross-out factor, says Techtmann, “that I think needs to be overcome.”
The military isn't the only institution working to turn microbes into food. From Korea to Finland, a small number of researchers and even a few companies are studying whether microorganisms could one day help feed the world's growing population.
Two birds with one stone
According to Tender, DARPA's solicitation aimed to solve two problems at once. First, the agency hoped to reduce what it called supply chain vulnerability: During a war, the military must transport supplies to troops in remote areas, posing a safety risk to the people in the vehicles. In addition, the agency wanted to end the use of dangerous burn pits to dispose of plastic waste. “Responsibly removing these waste products from these sites is a tremendous help,” Tender said.
Michigan Tech's system starts with a mechanical shredder that breaks the plastic into small shards, which then go into a reactor where they soak in ammonium hydroxide at high heat. Some plastics, such as PET, often used to make disposable water bottles, break down at this point. Other plastics used in military food packaging – namely polyethylene and polypropylene – are sent to another reactor where they are exposed to much higher heat and a lack of oxygen.
Under these conditions, polyethylene and polypropylene are converted into compounds that can be further processed into fuels and lubricants. David Shonnard, a chemical engineer at Michigan Tech who oversaw this part of the project, has founded a startup company called Resurgent Innovation to commercialize some of the technology. (Other members of the research team, Shonnard said, are seeking additional patents for other parts of the system.)